Computer disk drives store and retrieve data by using a magnetic read/write head positioned over a rotating magnetic data storage disk. The head writes data onto the disk by aligning magnetic poles set in concentric tracks on the disk. The width of the tracks depends on the width of the read/write head used. The narrower the tracks can be made, the more data which can be stored on a given disk. As the size of read/write heads have become progressively smaller in recent years, track widths have decreased. This decrease has allowed for dramatic increases in the recording density and data storage of disks.
In a typical disk drive, the magnetic head is supported and held above the disk surface by an actuator arm. By moving back and forth, the actuator operates to position the head above the disk to read or write data on a desired track. The actuator arm is typically moved by a voice coil motor (VCM) acting as a primary actuator. The problem which has arisen as track widths have decreased, is that the limits of the VCM""s positioning precision have begun to be reached. This limited precision has made it increasingly difficult to achieve accurate head positioning. As such, a need has arisen for a means to more precisely position read/write heads.
One approach to achieving finer head positioning has been to employ a secondary actuator to operate together with the primary actuation provided by the VCM. This approach involves placing a microactuator along the length of the actuator arm and configured the arm so the microactuator moves a portion of the arm containing the read/write head. Specifically, the head suspension assembly (HSA) of the actuator arm is divided into a fixed portion and a movable portion. Microactuators are connected between the two portions and positioned to be capable of moving the movable portion of the HSA. Thus, the VCM acts as a coarse actuator and the microactuator as a fine actuator.
Commonly, the microactuators have utilized piezoelectric materials which vary their length when a voltage is applied to them. As shown in FIG. 1, a widely used configuration is an actuator arm 2 which has two piezoelectric actuators 4 mounted between the base plate 6 and the load beam 8. The piezoelectric actuators 4 are positioned about a hinge 7 separating the base plate 6 and the load beam 8.
In this arrangement, the actuators 4 act in a xe2x80x98push-pullxe2x80x99 manner to move the load beam 8 relative to the base plate 6. That is, as one actuator 4 constricts and pulls the load beam 8 in the desired direction, the opposing actuator 4 expands to push the load beam 8 in the same direction. At the outboard end of the load beam is mounted a slider 9 which carries a read/write head. As can be in FIG. 1, the actuator arm 2 holds the slider 9 above a disk and by swinging side-to-side, move the slider 9 over the surface of the disk. In turn, the slider 9 positions the read/write head just above the disk surface by flying in the thin airflow layer created by the rotating disk. In so doing, the slider and the head are both kept very close to the disk surface. As the actuator arm 2 is swung back and forth, the movement imparted to the slider 9 is in a plane parallel to the plane of disk""s surface. As such, the slider 9 can be moved by the actuator arm 2 for relatively large displacements across the disk and can be moved by the piezoelectric actuators 4 for relatively small displacements.
Some significant disadvantages are inherent with this type of actuator arm. The primary disadvantage is out-of-plane movements which are imparted upon the slider 9 by the movement of the actuators 4. The out-of-plane motions are due to a deformation of the structure of the load beam 8 which occurs when the actuators 4 pull and push on the load beam 8. As a result, as the load beam 8 is moved and deformed by the actuators 4, the slider 9 is both moved across the disk surface and rolled to a certain degree. This rolling may cause one side of the slider to drop closer to the disk surface, which can cause a possible contact with the disk surface. As a result, such contact can damage the data tracks on the disk and decrease the disk drive""s overall performance. Clearly, such damage and reduced performance must be avoided.
Another limiting factor to these microactuator designs is that the relatively short displacement stroke of the push-pull piezoelectric actuators arrangement results in limited displacement of the read/write head. As such, these microactuator designs are limited to track following operations and cannot seek data tracks on their own.
Thus, a device is sought which will provide sufficient and precise in-plane motion of the read/write head to augment the displacements from the VCM, allowing for the fine head positioning needed with smaller track widths.
The present invention is embodied in an actuator arm which utilizes microactuators to provide fine positioning of a read/write head to supplement larger displacements from a primary actuator. A read/write head is mounted to the actuator arm and is displaced by the microactuators along an at least nearly straight line transverse to the longitudinal axis of the actuator arm. This transverse motion allows the read/write head to be kept substantially within a plane parallel to the surface of the data storage disk. This is a great advantage as no out-of-plane motion is imparted on the read/write head during the fine actuation, thus avoiding damage due to possible contact between slider and the disk surface. Another advantage is provided by the use of bimorph actuators which provide greater displacements to the read/write head than the displacements typically achieved from use of piezoelectric actuators in a push-pull configuration. Still another advantage is achieved from the transverse motion imparted to the head from the microactuators, as the amount of lateral displacement of the head is no longer a function of microactuator""s position along the actuator arm (as is the case with pivoting push-pull actuators in which the lateral head displacement is directly dependent on the distance between the actuators and the head). Since the displacement of the head is not adversely affected by the location of the microactuators on the actuator arm, the actuator arm can be made shorter, allowing the disk drive to be made more compact.
The actuator arm is attached to a primary actuator (e.g. a voice coil motor (VCM)) so the actuator arm and read/write head can be moved across the data storage disk. The actuator arm includes an inboard portion, an outboard portion and a pair secondary actuators. The secondary actuators are bimorph actuators. The inboard portion has a longitudinal axis and is attached to the primary actuator. The outboard portion has the read/write head mounted onto it. The pair of bimorph actuators are deflectable together in a common direction and are connected between the inboard and the outboard portions. Upon deflection of the bimorph actuators in the same direction, the outboard portion is translated along an at least nearly straight line transverse to the longitudinal axis of the inboard portion.
The outboard section can be moved to either side of the inboard portion. That is, the bimorph actuators can be deflected to cause the outboard section to translate to either side of the longitudinal axis of the inboard portion. The bimorph actuators can each include first and second piezoelectric layers. The layers are mounted longitudinally adjacent each other. Each actuator has electrical interfaces positioned to allow voltages to be applied to them. Thus, one layer is lengthened while the other is shortened, to cause the actuator to deflect in a direction towards the shortened layer. With the two bimorph actuators positioned substantially parallel to one another, a deflection in the same direction of both actuators will cause the outboard portion to move in a substantially linear direction. With the two bimorph actuators set at an angle (not parallel) to one another, the outboard portion will rotate as well as translate when moved by the actuators.
The actuator arm can be configured such that the read/write head is displaced to either side by at least the width of a single data storage track, or several tracks as needed. Also, the actuator arm can be configured such that the read/write head will be moved by the bimorph actuators substantially in a plane at least nearly parallel to the surface of the data storage disk.
The bimorph actuators can each have a first end and a second end, where the first end is mounted to the inboard portion of the actuator arm in a fixed manner to prevent rotation, and the second end is rotatably mounted to the outboard portion. This mounting allows the bimorph actuators to deform in a cantilever mode, and the outboard portion to translate along an at least nearly straight line transverse to the longitudinal axis. Alternatively, the first end can be rotatably mounted to the inboard portion and the second end can be mounted to the outboard portion in a fixed manner to prevent rotation. This alternate configuration also moves the outboard portion along an at least nearly straight line transverse to the longitudinal axis.
In one embodiment of the invention, the actuators are xe2x80x98s-shapedxe2x80x99 bimorphs. With a s-shaped actuator the bimorph actuators each include an inboard portion and an outboard portion. Each of these portions has two piezoelectric layers mounted longitudinally adjacent to each other with opposite polarization. The inboard and outboard portions are aligned and positioned such that the arrangement of the piezoelectric layers of the inboard portion are the opposite of that of the outboard portion. Each actuator has electrical interfaces positioned to allow voltages to be applied to them. The actuators are therefore configured such that when a voltage is applied to each, the actuators deflect into s-shaped beams. With such s-shaped bimorph actuators, ends of the actuators are mounted in a fixed manner to prevent their rotation.
In another embodiment of the invention, each secondary actuator is a single layer of piezoelectric mounted along a support member of a bendable length of non-piezoelectric material. In this embodiment, the shortening or lengthening of the piezoelectric relative to the connected constant length bendable support member causes the combination to bend in one direction or the other. For example, as the piezoelectric is shortened, the bendable member will be bent in the direction of the piezoelectric and if the piezoelectric is lengthened, the bendable member will be bent in the direction away from the piezoelectric. This deformable material can be metal. The deformable material can also be part of the structure of the actuator arm, such that the deformable material will function both to support the actuator arm and as part of the actuators which can deflect the outboard portion of the actuator arm.
The actuator arm can also include a voltage source and a voltage controller for applying voltages across the electrical interfaces of the actuators. This application of a voltage allows each first layer to be deformed an equal amount and each second layer to be deformed an equal amount which is separate from that of the first layers. As such, the first layers are deformed differentially from the second layers to cause the bimorph actuators to bend.
In one embodiment, the actuator arm can include a support arm and a suspension assembly. The suspension assembly being attached to the support arm at a swage point. The suspension assembly including a base plate at the swage point and a load beam separate from the base plate and extending out therefrom. Between the base plate and the load beam are a substantially parallel pair of two-layer piezoelectric bimorph actuators deflectable together in a common direction. Upon deflection of the actuators in the same direction, the load beam (which carries the slider and magnetic head) is translated along an at least nearly straight line transverse to the longitudinal axis of the actuator arm. The load beam moving substantially in a plane at least nearly parallel to the substantially planar surface of the data storage disk.